CN114034915A

CN114034915A - Miniature intelligent current sensor in bidirectional data transmission mode

Info

Publication number: CN114034915A
Application number: CN202111158809.3A
Authority: CN
Inventors: 余瑜; 王愚; 刘炳亮; 许鹏飞; 褚健; 李佩; 江雄勇; 邓高峰; 黄勇; 赵旭强; 莫绍康
Original assignee: Nanning Power Supply Bureau of Guangxi Power Grid Co Ltd
Current assignee: Nanning Power Supply Bureau of Guangxi Power Grid Co Ltd
Priority date: 2021-09-30
Filing date: 2021-09-30
Publication date: 2022-02-11

Abstract

The invention provides a miniature intelligent current sensor in a bidirectional data transmission mode, which comprises a measuring end and a control end, wherein the measuring end is connected with the control end; the measuring end converts the voltage signal into an analog current signal, loads a first FSK signal and then sends the analog current signal and the FSK signal to the control end through a transmission channel; the control end receives the analog current signal and the first FSK signal sent by the measuring end respectively, and sends a second FSK signal to the measuring end through the transmission channel. The FSK signal is loaded on the analog current transmission channel, so that the digital signal can be transmitted in a long-distance two-way manner, the original analog transmission channel is not damaged, and the FSK signal measuring system is compatible with the original measuring system; the main information of the measuring system can be transmitted, and other information of the measuring system can also be transmitted through digital information transmitted in two directions; the measurement system is adjusted on line by the bidirectional transmission of data, thereby effectively solving the problems and the defects of the invention in the background technology.

Description

Miniature intelligent current sensor in bidirectional data transmission mode

Technical Field

The invention relates to the technical field of sensors, in particular to a miniature intelligent current sensor in a bidirectional data transmission mode.

Background

In a measuring system, various non-electric physical quantity parameters measured by the sensor on site can be sent to a local system for processing or sent to a remote system for processing and application. When signals are transmitted in a long distance, certain errors and interference can be generated on the wires if voltage signals are used for transmitting information due to the fact that the wires are provided with resistors.

Therefore, usually, the measured electrical parameters are converted into current signals for long-distance transmission, and after a long time of development, for example, a 4-20 mA current signal transmission channel becomes a long-distance electrical signal transmission standard used in industry, and at present, in industrial production, 4-20 mA current signals and digital signals are stored in long-distance information transmission.

Nowadays, with the development of intelligent technology in industrial production, higher requirements are placed on a measuring system, the measuring system can meet more requirements due to the addition of an intelligent processing function, and the measuring system not only needs to achieve the purpose of measurement, but also needs to be adjusted online sometimes. The prior art does not meet such a need.

Therefore, there is a need to improve the prior art, and based on 4 to 20mA signal transmission, digital signal communication with a small data volume is performed in a way of sharing a channel while the 4 to 20mA signal transmission is performed.

Disclosure of Invention

The invention aims to provide a miniature intelligent current sensor in a bidirectional data transmission mode, which can solve the problem that the measurement cannot be simultaneously carried out on-line adjustment in the prior art.

The purpose of the invention is realized by the following technical scheme:

a miniature intelligent current sensor with a bidirectional data transmission mode comprises a measuring end and a control end; the measuring end converts the voltage signal into an analog current signal, loads a first FSK signal and then sends the analog current signal and the FSK signal to the control end through a transmission channel; the control end receives the analog current signal and the first FSK signal sent by the measuring end respectively, and sends a second FSK signal to the measuring end through the transmission channel.

Furthermore, the measuring end comprises a sensor, a first A/D conversion module, a first controller, a D/A conversion module and a first modem; the input end of the sensor collects signals, the output end of the sensor is connected with the input end of the A/D conversion module, the A/D conversion module converts the signals collected by the sensor into voltage signals and then sends the voltage signals to the input end of the first controller through the output end, the first output end of the first controller is connected with the first input end of the first modem, and the second output end of the first controller outputs the voltage signals to the first input end of the D/A conversion module; a second input end of the first modem receives a second FSK signal sent by the control end, and the first modem processes the received second FSK signal into a first FSK signal and sends the first FSK signal to a second input end of the D/A conversion module through an output end; the D/A conversion module converts the voltage signal sent by the first controller into an analog current signal, and then sends the analog current signal and a first FSK signal sent by the first modem to the control end through a transmission channel.

Furthermore, the control end comprises a second controller, a second A/D conversion module, a second modem and an alternating current driving circuit; the input end of the second A/D conversion module receives an analog current signal sent by the measuring end, and the first input end of the second modem receives a first FSK signal sent by the measuring end; the output end of the second A/D conversion module is connected with the input end of a second controller, and the output end of the second controller is connected with the second input end of a second modem; the output end of the second modem outputs a second FSK signal to the input end of the alternating current driving circuit, and the alternating current driving circuit converts the second FSK signal sent by the second modem into a current signal and sends the current signal to the measuring end through the transmission channel.

Furthermore, the transmission channel is a 4-20 mA current transmission channel.

Furthermore, the D/A converter at least comprises a first controller at least comprising a digital signal pin, a clock signal pin and a latch pin, wherein the digital signal pin is connected with the first controller through a data line; the clock signal pin is connected with the first controller through a clock line; the latch pin is connected with the first controller through a latch line.

Further, the second a/D conversion module includes an inductor L2, a resistor R1, and a capacitor C5, one end of the inductor L2 is connected to the transmission channel, and the first FSK signal superimposed on the analog current signal is filtered by the inductor L2; an analog current signal sent by the measuring end passes through an inductor L2 and then is input to one end of a resistor R1, the other end of the resistor R1 is grounded, a capacitor C5 is connected in parallel to two ends of a resistor R1, and one end of a resistor R1 is connected to a second controller.

Further, the first modem at least comprises a digital signal output pin, a digital signal input pin, a sending request pin, a carrier detection output pin and an FSK signal output pin; the digital signal output pin, the digital signal input pin, the sending request pin and the carrier detection output pin are respectively connected with the first controller; the first controller detects the level value of the carrier detection output pin, and when the carrier detection output pin is at a high level, the first controller enters a receiving state; the FSK signal output pin outputs an FSK signal to the D/A conversion module.

Further, a slide rheostat R20 and a capacitor C30 are further included between the FSK signal output pin and the first controller, the FSK signal output pin is connected with one end of the slide rheostat R20, the other end of the slide rheostat R20 is grounded, and the movable end of the slide rheostat R20 is connected with the capacitor C30 in series and then connected to the D/A conversion module.

According to the miniature intelligent current sensor in the bidirectional data transmission mode, the miniature intelligent current sensor in the bidirectional data transmission mode is improved, and an FSK signal is loaded on the analog current transmission channel, so that a digital signal can be bidirectionally transmitted in a long distance without damaging the original analog transmission channel, and the miniature intelligent current sensor is compatible with an original measurement system; the main information of the measuring system can be transmitted, and other information of the measuring system can also be transmitted through digital information transmitted in two directions; the measurement system is adjusted on line by the bidirectional transmission of data, thereby effectively solving the problems and the defects of the invention in the background technology.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the description of the embodiments or the prior art will be briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.

FIG. 1 is a schematic diagram of a frame structure of a measurement side circuit according to the present invention;

FIG. 2 is a schematic diagram of a control end circuit framework according to the present invention;

FIG. 3 is a schematic diagram of the peripheral circuit connection of the D/A converter according to the present invention;

FIG. 4 is a schematic diagram of a digital interface circuit of the D/A converter and the first controller according to the present invention;

FIG. 5 is a circuit diagram of a second A/D conversion module according to the present invention;

FIG. 6 is a pin diagram of a first modem and a second modem of the present invention;

FIG. 7 is a functional block diagram of a first modem and a second modem of the present invention;

fig. 8 is a schematic diagram of the demodulation process of the first modem and the second modem according to the present invention;

FIG. 9 is a schematic diagram of crystal oscillators within the first modem and the second modem of the present invention;

FIG. 10 is a schematic diagram of the oscillators of the external clock to which the first modem and the second modem are connected according to the present invention;

fig. 11 is a diagram of peripheral circuit connections for a first modem and a second modem of the present invention;

FIG. 12 is a circuit diagram of a first controller and a first modem according to the present invention;

fig. 13 is a peripheral circuit diagram of a first modem and a D/a conversion module of the present invention;

FIG. 14 is a connection diagram of a remote control receiving circuit according to the present invention;

FIG. 15 is a connection diagram of the near-end measurement site transceiver circuit of the present invention.

Detailed Description

The embodiments of the present disclosure are described in detail below with reference to the accompanying drawings.

The embodiments of the present disclosure are described below with specific examples, and other advantages and effects of the present disclosure will be readily apparent to those skilled in the art from the disclosure in the specification. It is to be understood that the described embodiments are merely illustrative of some, and not restrictive, of the embodiments of the disclosure. The disclosure may be embodied or carried out in various other specific embodiments, and various modifications and changes may be made in the details within the description without departing from the spirit of the disclosure. It is to be noted that the features in the following embodiments and examples may be combined with each other without conflict. All other embodiments, which can be derived by a person skilled in the art from the embodiments disclosed herein without making any creative effort, shall fall within the protection scope of the present disclosure.

The invention relates to a miniature intelligent current sensor in a bidirectional data transmission mode, which comprises a measuring end at the near end and a control end at the far end; the measuring end converts the voltage signal into an analog current signal, loads a first FSK signal and then sends the analog current signal and the FSK signal to the control end through a transmission channel; the control end receives the analog current signal and the first FSK signal sent by the measuring end respectively, and sends a second FSK signal to the measuring end through the transmission channel.

The measuring end comprises a sensor, a first A/D conversion module, a first controller, a D/A conversion module AD421 and a first modem; the input end of the sensor collects signals, the output end of the sensor is connected with the input end of the A/D conversion module, the A/D conversion module converts the signals collected by the sensor into voltage signals and then sends the voltage signals to the input end of the first controller through the output end, the first output end of the first controller is connected with the first input end of the first modem, and the second output end of the first controller outputs the voltage signals to the first input end of the D/A conversion module; a second input end of the first modem receives a second FSK signal sent by the control end, and the first modem processes the received second FSK signal into a first FSK signal and sends the first FSK signal to a second input end of the D/A conversion module through an output end; and after converting the voltage signal sent by the first controller into an analog current signal, the D/A conversion module and the FSK signal sent by the first modem are sent to the control end together through a 4-20 mA current transmission channel.

The remote control end comprises a second controller, a second A/D conversion module, a second modem and an alternating current driving circuit; the input end of the second A/D conversion module receives an analog current signal sent by the first controller of the measuring end, and the first input end of the second modem receives an FSK signal sent by the first controller of the measuring end. The output end of the second A/D conversion module is connected with the input end of the second controller, and the output end of the second controller is connected with the second input end of the second modem. The output end of the second modem outputs FSK signals to the input end of the alternating current driving circuit, and the alternating current driving circuit converts the FSK signals sent by the second modem into current signals and finally sends the current signals to the measuring end through the output end and a 4-20 mA current transmission channel.

In a specific embodiment of the present application, the MSP430F149 single chip microcomputer is selected as the first controller and the second controller. The D/A conversion module adopts AD421 of 4-20 mADACs. The AD421 is internally provided with an optional voltage stabilizer for supplying power to the AD421 and other devices in transmission, the voltage stabilizer can provide +5V, +3.3V and +3V regulated output voltage, the devices are also internally provided with +1.25V and +2.5V precision reference voltage sources, therefore, the AD421 does not need to be externally connected with an independent voltage stabilizer and a reference voltage source, external elements only need a plurality of passive elements and an adjusting tube and are used for expanding the voltage range of a loop, the AD421 can be used by combining with a standard HARTSK protocol communication circuit, an access point of an FSK signal is provided so that the FSK signal and an analog current signal of 4-20 mA can be transmitted simultaneously through a shared channel, and the rated performance cannot be influenced.

As shown in fig. 6, the first modem and the second modem use a5191HRT, which is a monolithic CMOS modem that is a field instrument for high-speed addressable remote sensors. The FSK half-duplex working mode with continuous phase is adopted, the data rate is 1200bps, circuits such as a modulator, a demodulator, a receiving filter, a sending signal shaping circuit and carrier detection which accord with the Bell202 standard are integrated in the A5191HRT, the working current is 330uA when power is supplied at 3.3V, due to the characteristics of the A5191HRT, a designer can construct a circuit meeting the requirements of an HART protocol physical layer by using fewer external passive elements, the A5191HRT and the SYM20C15 are compatible in pins, and the SYM20C15 can be used for a modem chip designed by the circuit.

As shown in fig. 7, the internal circuitry for a5191HRT includes a transmit data modulator and shaper, carrier detect circuitry, analog receive and demodulator circuitry, and a crystal oscillator.

As shown in fig. 7 and 8, this modulator receives digital data in NRZ format from the ITXD input port and generates an FSK modulated signal to be output from the OTXA port. The INRTS port must be low to allow the modulator to operate. While the demodulator receives the FSK signal from the IRXA input port and reproduces the original modulated signal at the ORXD output. The normal bit rate is 1200 bits per second. The output of the demodulator is a qualified carrier detect signal (OCD) so that serial data received at ORXD can only be generated if the IRXA signal is large enough to be detected by the carrier detect circuit.

The a5191HRT transmit signal waveform shaper generates a HART compatible FSK modulated signal at the OTXA end. When IAREF =1.235V_DCOTXA will have a voltage with a waveform amplitude of about 0.25V to 0.75V. Namely the peak-to-peak value of the FSK sine wave signal emitted by the A5191HRT is 0.5V_p-p。

Analog receiving circuit of a5191 HRT:

A. reference voltage

IAREF sets the dc operating point of the internal operational amplifier and comparator. A DC reference voltage of 1.235V (ADI AD589) was used for IAREF.

The level at which the OCD port (carrier sense) is activated is determined by the dc voltage difference (IAREF-ICDREF). Selecting a DC voltage difference of 0.08V will set the carrier sense to 100mV_p-p。

B. Bias current resistor

The a5191HRT requires a bias current resistor to be connected between OCBIAS and VSS. The bias current controls the operating parameters of the internal operational amplifier and comparator.

The resistance value of the bias current is determined by the reference voltage IAREF and the following equation:

when IAREF is equal to IAREF-1.235V_DCThen, a bias current resistor of 500K Ω is recommended.

Crystal oscillator As shown in FIG. 9, the A5191HRT requires a 460.8kHz clock signal at the OXTL terminal. This may be provided by an external clock or may be connected to the a5191HRT internal oscillator external components.

Alternatively, an internal crystal oscillator may be used, and the oscillator unit may be operated with a 460.8khz crystal or ceramic resonator. The ceramic resonator can be parallel-resonant between OXTL and IXTL. Because of the high cost of ceramic oscillators and its low availability, embodiments of the present application use an external 460.8kHz clock. When an external clock is used, a5191HRT consumes less current. When the clock is connected to OXTL and IXTL is connected to VSS, the current consumption is the lowest.

The first controller and the second controller control the work of the whole circuit, the AD421 realizes digital-to-analog conversion and generates 4-20 mA current, and the A5191HRT completes the work of modulation and demodulation; the long-distance transmission channel of the signal uses twisted-pair wires.

Specifically, the first controller at the measuring end takes an MSP430F149 single chip microcomputer as a control device; the first controller completes four jobs:

firstly, transmitting a digital signal to a D/A conversion module AD421, so that the AD421 converts the digital signal into a standard analog current signal for remote transmission;

secondly, controlling the working mode of a first modem A5191 HRT;

thirdly, receiving the signal demodulated by the first modem A5191 HRT;

and fourthly, controlling the on-off state of the relay.

Specifically, the second controller of the remote control end takes an MSP430F149 single-chip microcomputer as a control device; the control device completes four tasks:

firstly, controlling the work of a second modem A5191 HRT;

secondly, simultaneously receiving the signal demodulated by the second modem A5191 HRT;

thirdly, controlling the on-off state of the relay;

and fourthly, receiving the voltage signal converted from the 4-20 mA current signal to the far end, and processing the voltage signal.

The alternating current driving circuit is responsible for converting FSK voltage signals output by the second modem A5191HRT into current signals which can be transmitted at a long distance.

As shown in FIG. 3, in the peripheral circuit design of the D/A conversion module AD421, the 4 th pin LV of the D/A conversion module is connected to the 16 th pin Vcc through a 0.01uF capacitor C23, and the regulated voltage is 3.3V. The voltage regulator of the AD421 supplies power to the D/a conversion module AD421 and other components of the transmitter through a 16 th pin Vcc together with the adjusting transistor ND 2020L. The Vcc pin should be sufficiently decoupled using a 2.2uF capacitor C22 to ensure stable operation of the regulator and absorb supply glitches on the Vcc line of AD421 and other devices in the system, in order to stabilize the feedback loop formed by the operational amplifier and external regulation circuitry in the voltage regulator, not only capacitor C26 of 0.01uF is connected between pin COMP 14 and pin DRIVE 13, but also 1K of resistor R19 and 1000pF capacitor C28 are connected between DRIVE and ground and COM and ground. A2 nd pin REFUT 2 of an AD421 internal 2.5V reference source is directly used as a 3 rd pin REFIN input reference voltage and is externally connected with a 4.7uF decoupling capacitor C24. The on-chip DAC is connected with a time sequence filter in a rear-connection mode, three capacitors which are absorbed by low dielectric substances need to be connected externally, a 12 th pin C1 is connected with a capacitor C31 externally, a 11 th pin C2 is connected with a capacitor C29 externally, and a 10 th pin C3 is connected with a capacitor C30 externally. C31 ═ C29 ═ 0.01uF and C30 ═ 0.0033uF are typical.

The AD421 digital interfaces have three, pin 7 DATA, pin 6 CLOCK and pin 5 LATCH, which can be directly connected to the first controller. The DATA of the DATA interface is loaded at the rising edge of the CLOCK CLOCK, and is input into the shift register, and is loaded into the DAC LATCH at the rising edge of LATCH LATCH control. The current output by the DAC passes through the current amplifier part, and 4-20 mA of current is output from an 8 th pin LOOPRTN interface.

As shown in fig. 4, the D/a conversion module AD421 is connected to the digital interface of the first controller MSP430F149, the AD421 is connected to the serial SPI port of the first controller MSP430F149, the 7 th pin of the D/a conversion module is a digital signal pin DATA, and the 7 th pin is connected to the 45 th pin P5.1/SIMO1 of the first controller through a DATA line. The 6 th pin of the D/A conversion module is a CLOCK signal pin CLOCK, the 6 th pin is connected with the 47 th pin P5.3/UCLK1 of the first controller through a CLOCK line, the 5 th pin of the D/A conversion module is a LATCH pin LATCH, and the 5 th pin is connected with the 46 th pin P5.2/SOMI1 of the first controller through a LATCH line.

As shown in fig. 5, the circuit design of the 4-20 mA current receiving end is such that the 4-20 mA current is transmitted in a long distance to the terminal, converted into a voltage by the second a/D conversion module, and then transmitted to the a/D end of the second controller, and the single chip microcomputer responds accordingly according to the received voltage signal. The second A/D conversion module comprises an inductor L2, a resistor R1 and a capacitor C5, and an FSK sine wave signal superposed on a 4-20 mA current signal is blocked by an inductor L2. 4-20 mA analog current signals and FSK signals sent by the measuring end are input to one end of a resistor R1 after passing through an inductor L2, the other end of the resistor R1 is grounded, a capacitor C5 is connected to two ends of a resistor R1 in parallel, and one end of a resistor R1 is connected to a second controller.

The calculation formula of the ADC conversion module result of the second controller MSP430F149 singlechip is as follows:

wherein, V_INEqual to the input analogue voltage, V_R+Positive voltage of reference voltage, V_R-Is a negative voltage (typically 0V) of the reference voltage.

When the input voltage V_IN≥V_R+Then, the ADC outputs a full scale value of 0 FFFH; when the input voltage V_IN≤V_R-While, the ADC outputs 0. If the single chip is expected to effectively process the voltage signal, the value of the input voltage is V_R-And V_R+In the meantime.

The known single chip ADC has a reference voltage generator, and can provide reference voltages of 1.5V and 2.5V. Here we take V_R+＝2.5V，V_R-As can be seen from the above condition, the analog input voltage of the ADC cannot exceed 2.5V.

The selected resistance R1 is equal to 100 omega, then

4～20mA×100Ω＝0.4～2V

Obviously, the voltage does not exceed 2.5V, i.e., the resistance is selected to meet the circuit design requirements.

The resistor R1 is connected across the capacitor C5 to ground, which grounds the AC path. Generally, a capacitor of about 10pF is used for filtering out high-frequency interference signals, and a capacitor of about 0.1uF is used for filtering out low-frequency ripple interference. In the circuit, in order to filter signals of 1200Hz and 2200Hz, a capacitor with C5 equal to 0.001uF is selected as a filter capacitor.

For the choice of inductance L2, due to the impedance:

Z=2πfl

two frequencies of the FSK signal:

f₁=1200Hz,f₂=2200Hz

then, the inductance L2 is selected to be 1000mH, and the impedance corresponds to two frequencies:

Z₁=2πf₁l=7536Ω

Z₂=2πf₂l=13816Ω

therefore, the corresponding impedance is large enough to block the alternating current, that is, the selected inductor size meets the design requirement.

As shown in fig. 11, the first modem a5191HRT chip peripheral circuit is connected, and the first controller MSP430F149 singlechip also controls the operation mode of the first modem a5191 HRT.

As shown in fig. 12, as can be seen from fig. 11, the 25 th pin ORXD (digital signal output pin) of the first modem is connected to the receiving end (33 th pin P3.5) of the asynchronous communication port of the first controller, the 23 th pin ITXD (digital signal input pin) of the first modem is connected to the receiving end (32 th pin P3.4) of the asynchronous communication port of the first controller, the 22 th pin INRTS (transmission request pin) of the first modem is connected to the 26 th pin P2.6 of the first controller, and the 26 th pin OCD (carrier detect output pin) of the first modem is connected to the 27 th pin P2.7 of the first controller. When the host device sends a command from the serial communication port, the FSK signal on the current loop is sent to the first modem a5191HRT at the near end, the receiving filter of the first modem a5191HRT performs filtering and demodulation, the FSK signal is demodulated into digital signals of "0" and "1", the digital signals are output to the first controller from the 25 th pin (digital signal output pin) ORXD, and after the first controller receives the signals, the signals are subjected to command analysis, and then corresponding operations are performed. The 26 th pin OCD is the carrier sense output and the OCD terminal goes high when the IRXAC detects a valid input, so the first controller enters the receive state by detecting the first modem OCD pin. The INRTS, pin 22 of the first modem is a request to send pin, and when low, the modulator is on and the demodulator is off. The modulator module receives the non-return-to-zero digital signal input from the ITXD pin, generates an FSK modulated signal, and outputs the FSK modulated signal from the 7 th pin OTXA pin (FSK signal output pin) of the first modem, as shown in the circuit connection diagram of fig. 12.

As shown in fig. 13, as can be seen from fig. 11 and 12, the FSK signal generated by the first modem is output by the OTXA pin. The FSK signal is coupled to the AD421 through a pin C3 of the D/A conversion module AD421, so that the FSK signal is loaded to a 4-20 mA current signal for remote transmission, which is shown in a circuit connection diagram of FIG. 13.

The voltage signal output by the 7 th pin OTXA of the first modem is a sine wave voltage signal of 0.25V-0.75V. I.e. its peak to peak value is 0.5V_p-p. When the peak value of the output peak is 0.5V_p-pVoltage signal, current coming out of the loprtn pin:

current peak value:

obviously, if a current with a peak value of 6.25mA is superposed on a current channel with a peak value of 4-20 mA, a clipping phenomenon can occur, and the situation is not allowed to occur in a circuit. And according to the HART protocol, the amplitude of the overlapped FSK signal is 0.5mA, and in the circuit, the peak-to-peak value of the FSK sine wave signal overlapped on the 4-20 mA current signal is determined as follows:

I=1mA

p-p

therefore, voltage division is carried out in the circuit by using a slide rheostat R20, R20 selects a slide rheostat with the resistance value of 5.1K omega, and the overlapped FSK signal is I by adjusting the movable end of the slide rheostat_p-p=1 mA. The moving end of the slide rheostat is connected to the 10 th pin C3 of the D/A conversion module through a capacitor C30.

As shown in fig. 14 and fig. 15, both relays are connected to P1.2 pins of two MSP430F149 singlechips, respectively, and the on/off of the relays are controlled according to the high and low levels output by the singlechips. The relay is driven by a transistor Q1, the emitter of which must be connected to ground. When the base of the transistor Q1 is input with high level, the transistor is in saturation conduction; when the base of the transistor is inputted with a low level, the transistor is turned off. The transistor may be considered a control switch. The diode D1 freewheels in the reverse direction, suppresses the surge, and is normally closed when the relay is not operating.

The half-duplex working mode comprises the following process that when a near-end measuring system loads an FSK signal on a 4-20 mA current transmission channel, a first controller controls a near-end relay switch to be switched off, a far-end relay switch is switched on, the far-end FSK signal is transmitted to a demodulator input end IRXA of a first modem after passing through a transformer, and the signal is input into a single chip microcomputer for processing after being demodulated, wherein the process is the forward transmission process of the FSK signal. When the FSK signal is transmitted reversely, namely the first controller controls the FSK signal to be transmitted to the near end from the output of the second modem A5191HRT at the far end, the singlechip controls the relay switch at the far end to be disconnected, so that the FSK signal at the far end is processed by the alternating current driving circuit and then is transmitted to the transmission channel through the transformer, and the relay switch at the near end is closed, so that the circuit at the near end is in a state of receiving the FSK signal. The two pieces of A5191HRT do not receive FSK signals when sending the FSK signals; on the contrary, when receiving the FSK signal, the FSK signal is not transmitted. Under the control of the single chip microcomputer, the relay switch is in a correct switch state, and meanwhile, the single chip microcomputer gives an A5191HRT instruction to make the relay switch make a correct response. Thus realizing the coordinated operation of the whole circuit.

The circuit shown in fig. 14 receives an FSK signal transmitted from the near end and transmits an FSK signal of the far-end control site. The circuit shown in fig. 15 receives an FSK signal from a remote site. For convenience of calculation, the transformation ratios of the two transformers T1 and T2 shown in the figure are each selected to be 1: 1.

When the FSK signal is transmitted in the forward direction, the peak-to-peak value of the FSK sine wave signal superimposed on the 4-20 mA current signal is I_p-p=1mA, this FSK signal is from A5191HRTAnd receiving at an IRXA end. As can be seen from the requirement of the IRXA input pin of A5191HRT, the input signal of IRXA is usually 100mV_p-p。

To achieve this, the resistance across the remote transformer is known:

the capacitance C13 is sized as follows.

In order to increase the accuracy of the circuit, to reduce the amount of applied capacitance and to maximize the signal applied to the resistor, the FSK signal is applied to the circuit at two frequencies f₁And f₂1200HZ and 2200HZ, respectively, capacitive reactance

Then take C13=100uF,

then

According to the vector trigonometric relation, almost all the transmitted FSK signals are added to the resistors, and the selected resistors meet the requirements.

When the FSK signal is transmitted in reverse, i.e. the FSK signal is transmitted from the far end to the near end, the near end and the far end circuits have a certain symmetry when receiving the signal.

For the same reason as in the above calculation procedure, R28=100 Ω, C33=100uF are taken.

When the FSK signal is transmitted reversely, the A5191HRT is used for outputting the FSK signal which is a sine wave signal of 0.25V-0.75V, and a voltage signal is converted into a current signal to effectively transmit the signal to a far end when the signal is transmitted at a long distance. The alternating current driving circuit converts a sine wave signal of 0.25V-0.75V into a current signal and transmits the current signal to a near-end measuring end.

The peak-to-peak current value of the FSK alternating current signal transmitted is also set to be 1mA_p-pPeak-to-peak value of voltage signal is 0.5V_p-pAnd then:

the current signal is transmitted through transformer T1 for long distance to transformer T2 and to the IRXA port of a5191HRT for demodulation.

Assuming that the amplification factor β of the transistor is 16, R17 is equivalent to the base terminal, and the equivalent resistance is 8K Ω.

Selecting R15=4.7K Ω, R16=5,1K Ω as shown in fig. 14 places the amplifier in an amplified state.

In summary, the following steps: according to the miniature intelligent current sensor in the bidirectional data transmission mode, the miniature intelligent current sensor in the bidirectional data transmission mode is improved, and an FSK signal is loaded on a 4-20 mA analog current transmission channel, so that a digital signal can be bidirectionally transmitted in a long distance, an original analog transmission channel is not damaged, and the miniature intelligent current sensor is compatible with an original measuring system; the main information of the measuring system can be transmitted, and other information of the measuring system can also be transmitted through digital information transmitted in two directions; the measurement system is adjusted on line by the bidirectional transmission of data, thereby effectively solving the problems and the defects of the invention proposed in the background technology.

The above description is for the purpose of illustrating embodiments of the invention and is not intended to limit the invention, and it will be apparent to those skilled in the art that any modification, equivalent replacement, or improvement made without departing from the spirit and principle of the invention shall fall within the protection scope of the invention.

Claims

1. The miniature intelligent current sensor in the bidirectional data transmission mode is characterized by comprising a measuring end and a control end; the measuring end converts the voltage signal into an analog current signal, loads a first FSK signal and then sends the analog current signal and the FSK signal to the control end through a transmission channel; the control end receives the analog current signal and the first FSK signal sent by the measuring end respectively, and sends a second FSK signal to the measuring end through the transmission channel.

2. The smart miniature current sensor of claim 1, wherein said measurement terminal comprises a sensor, a first a/D conversion module, a first controller, a D/a conversion module and a first modem; the input end of the sensor collects signals, the output end of the sensor is connected with the input end of the A/D conversion module, the A/D conversion module converts the signals collected by the sensor into voltage signals and then sends the voltage signals to the input end of the first controller through the output end, the first output end of the first controller is connected with the first input end of the first modem, and the second output end of the first controller outputs the voltage signals to the first input end of the D/A conversion module; a second input end of the first modem receives a second FSK signal sent by the control end, and the first modem processes the received second FSK signal into a first FSK signal and sends the first FSK signal to a second input end of the D/A conversion module through an output end; the D/A conversion module converts the voltage signal sent by the first controller into an analog current signal, and then sends the analog current signal and a first FSK signal sent by the first modem to the control end through a transmission channel.

3. The smart miniature current sensor of claim 1, wherein said control terminal comprises a second controller, a second a/D conversion module, a second modem and an ac current driving circuit; the input end of the second A/D conversion module receives an analog current signal sent by the measuring end, and the first input end of the second modem receives a first FSK signal sent by the measuring end; the output end of the second A/D conversion module is connected with the input end of a second controller, and the output end of the second controller is connected with the second input end of a second modem; the output end of the second modem outputs a second FSK signal to the input end of the alternating current driving circuit, and the alternating current driving circuit converts the second FSK signal sent by the second modem into a current signal and sends the current signal to the measuring end through the transmission channel.

4. A bidirectional data transmission mode miniature intelligent current sensor as claimed in any one of claims 1 to 3, wherein said transmission channel is a 4-20 mA current transmission channel.

5. The smart miniature current sensor with bidirectional data transmission mode according to claim 2, wherein said D/a converter comprises at least a first controller comprising at least a digital signal pin, a clock signal pin and a latch pin, said digital signal pin being connected to said first controller via a data line; the clock signal pin is connected with the first controller through a clock line; the latch pin is connected with the first controller through a latch line.

6. The smart miniature current sensor according to claim 3, wherein said second A/D conversion module comprises an inductor L2, a resistor R1 and a capacitor C5, one end of the inductor L2 is connected to the transmission channel, and the first FSK signal superimposed on the analog current signal is filtered by the inductor L2; an analog current signal sent by the measuring end passes through an inductor L2 and then is input to one end of a resistor R1, the other end of the resistor R1 is grounded, a capacitor C5 is connected in parallel to two ends of a resistor R1, and one end of a resistor R1 is connected to a second controller.

7. The smart miniature current sensor for bidirectional data transmission mode of claim 2, wherein said first modem comprises at least a digital signal output pin, a digital signal input pin, a transmission request pin, a carrier detect output pin and an FSK signal output pin; the digital signal output pin, the digital signal input pin, the sending request pin and the carrier detection output pin are respectively connected with the first controller; the first controller detects the level value of the carrier detection output pin, and when the carrier detection output pin is at a high level, the first controller enters a receiving state; the FSK signal output pin outputs an FSK signal to the D/A conversion module.

8. The smart miniature current sensor according to claim 7, further comprising a sliding rheostat R20 and a capacitor C30 between said FSK signal output pin and said first controller, wherein said FSK signal output pin is connected to one end of a sliding rheostat R20, the other end of the sliding rheostat R20 is grounded, and the movable end of the sliding rheostat R20 is connected to the D/A conversion module after being connected to the capacitor C30 in series.